This invention relates generally to fluid powered vane type motors and more particularly to air powered engine starter motors.
Air or gas powered vane type motors are typically capable of very high rotational speeds. Because of these high speeds, and because of the moisture and other contaminants which are often found in compressed air systems, air motors typically require a supply of oil to provide lubrication and corrosion protection. Lack of an adequate oil supply typically results in rapid wear of the rotor, end plates, vanes, cylinder bore, and rotor shaft.
In air powered engine starter motors, this requirement for lubrication and corrosion protection is typically satisfied by a connection which bleeds diesel fuel into the air motor, or by an in-line lubricator. Either of these mechanisms provides a lubricant which, entrained in the compressed air, creates an oil mist which lubricates the moving parts of the air motor. Much of this lubricant is exhausted from the motor with the exhaust air.
Environmental protection requirements have become increasingly stringent over the past several years. This has generated a significant interest in achieving operation of air starter motors using a minimum of externally supplied lubrication.
Efforts to eliminate or reduce the need for lubrication have typically included hard facing of wear surfaces often coupled with superfinish surfaces to minimize friction. Another contribution to reduction of friction was achieved many years ago incidental to the replacement of metal vanes with fiber-reinforced polymeric vanes. This replacement was, at the time, motivated primarily by reductions of weight and cost of manufacturing.
Application of hard facing and polishing to achieve the previously mentioned superfinish significantly increases the manufacturing costs and the number of manufacturing operations required. Moreover, merely hardening and smoothing the wear surfaces of the unit will not eliminate wear. The friction experienced in high speed unlubricated operation can generate temperatures sufficient to soften, or even melt, the most refractory metals. Hence, it is not enough to merely harden and smooth the surfaces--a degree of lubricity must be introduced to the interface without adding an excess of external lubricant.
The foregoing illustrates limitations known to exist in present devices and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.